It has long been established that house mites (family Pyroglyphidae) are a source of house dust allergens that not only cause allergies but also adversely contribute to other pathologies, such as asthma. It has also been established that use of allergen control measures is effective in controlling these conditions. Allergen-proof encasing to contain mites to prevent allergen egress has long been used in bedding (mattresses, pillows, duvets, bed upholstery).
To the extent that such encasing comes in direct or indirect (i.e. through the bed sheets or pillowcase) contact with the human body, it is important that it be pleasant to the touch and moisture-vapor permeable. For aesthetic as well as for comfort reasons, it is important that the material have a good drape and not feel stiff. The prior art has variously attempted to solve these problems. For example:
Since about 1984, Allergy Control Products, Inc. has marketed bedding article encasings (e.g. mattress, tickings, pillow casings, and comforter covers) made of a cotton-polyester blend nonstretchable woven fabric (BOUNCE from Springs Mills, S.C.) laminated with a polyether polyurethane film (DEERFIELD 6100S) 1 mil thick. The lamination process for this material did not involve any stretching of either the film or the (nonstretch) substrate. These bedding article encasings had a moisture vapor transmission of about 100 to about 200 g/m.sup.2 /day when measured by ASTM E-96 (Procedure (B), "upright cup"). More recently, the same company has marketed bedding encasings made of a stretch-knit fabric (ADELE circular knit no. 8775, Adele Knits, Winston-Salem, N.C.) and laminated with a 1.0 mil thick film of a polyether polyurethane designated DUREFLEX 6100S (available from Deerfield Urethane Inc., South Deerfield, Mass.).
These later-commercialized encasings had the advantage of being elastic and provided a better fit. They also had a moisture vapor transmission of about 100-200 g/m.sup.2 /day (ASTM E-96). However, the drape of these encasings was still unsatisfactory.
U.S. Pat. No. 5,050,256 discloses bedding systems for mite-induced allergy control enclosed in a barrier material of polyurethane coated (not laminated) woven (nonstretch) fabric that is said to have high water vapor transmission properties. Coated materials suffer from the fact that the coating substance penetrates the fabric and causes it to stiffen. In addition, a relatively high amount of coating must be used to completely cover the fibers of the fabric (thus assuring allergen-barrier properties) which further compounds the stiffness (unsatisfactory drape) problem. Finally, it is not advisable to coat a stretch substrate because of difficulties in controlling the stretch knit under the coating head and because the coating interferes with the stretch properties of the material.